g++ demo.cpp -g -lSDL2 -lSDL2_ttf -framework OpenGL -lGLEW -o demo

demo.cpp

//From here but switched to 3.3 http://stackoverflow.com/questions/19748147/sdl-ttf-draws-garbage
#include <GL/glew.h>

#include <SDL2/SDL.h>
#include <SDL2/SDL_opengl.h>
#include <SDL2/SDL_ttf.h>

#include <string>
#include <iostream>

using namespace std;

SDL_Window *window = NULL;
SDL_GLContext context = NULL;
TTF_Font* font = NULL;
SDL_Surface* surface = NULL;

//OpenGL Objects
GLuint vao;
GLuint vbo;
GLuint texture;

//Shader Objects
GLuint program;
GLuint vs;
GLuint fs;

//Sampler Object
GLuint uniformSampler;


//The shaders are identical to yours
const string fragmentShaderString = 
                "#version 330\n" // My laptop can't do OpenGL 3.3 so 3.0 will have to do
                "in vec2 texCoord;\n"
                "in vec4 fragColor;\n"
                "\n"
                "out vec4 finalColor;\n"
                "\n"
                "uniform sampler2D myTextureSampler;\n"
                "void main() {\n"
                "  finalColor = texture( myTextureSampler, texCoord ) * fragColor;\n"
                "}";

const string vertexShaderString = 
                "#version 330\n"
                "\n"
                "in vec3 vert;\n"
                "in vec4 color;\n"
                "in vec2 texcoord;\n"
                "\n"
                "out vec4 fragColor;\n"
                "out vec2 texCoord;\n"

                "void main() {\n"
                "  fragColor = color;\n"
                "  gl_Position = vec4(vert, 1);\n"
                "  texCoord = texcoord;\n"
                "}\n";

//Your vertices, but I changed alpha to 1.0f
const GLfloat vertices[] = 
{
    //X    Y      Z     R     G     B     A     U    V
    -1.0f, -1.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.f, 1.f,
     1.0f, -1.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f, 1.f, 1.f,
    -1.0f, -0.4f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.f, 0.f,
     1.0f, -1.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f, 1.f, 1.f,
     1.0f, -0.4f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f, 1.f, 0.f,
    -1.0f, -0.4f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.f, 0.f
};

int main(int argc, char* args[])
{
  //Create Window and Context
  window = SDL_CreateWindow("SDL Text with OpenG", 0, 0, 640, 480, SDL_WINDOW_OPENGL);

  //Set Core Context
  SDL_GL_SetAttribute( SDL_GL_CONTEXT_MAJOR_VERSION, 3 );
  SDL_GL_SetAttribute( SDL_GL_CONTEXT_MINOR_VERSION, 3 );
  SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);

  context = SDL_GL_CreateContext(window);

  //Simple OpenGL State Settings
  glViewport( 0.f, 0.f, 640.f, 480.f);
  glClearColor( 0.f, 0.f, 0.f, 1.f);

  //Init Glew
  //Set glewExperimental for Core Context
  glewExperimental=true;
  glewInit();

  //Set Blending 
  //Required so that the alpha channels show up from the surface
  glEnable(GL_BLEND);
  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

  

  //Create Shaders
  vs = glCreateShader(GL_VERTEX_SHADER);
  fs = glCreateShader(GL_FRAGMENT_SHADER);

  //Source Pointers
  const GLchar* vsSource= &vertexShaderString[0];
  const GLchar* fsSource = &fragmentShaderString[0];

  //Set Source
  glShaderSource(vs, 1, &vsSource, NULL);
  glShaderSource(fs, 1, &fsSource, NULL);

  //Compile Shaders
  glCompileShader(fs);
  glCompileShader(vs);

  //Create Shader Program
  program = glCreateProgram();

  //Attach Shaders to Program
  glAttachShader(program, vs);
  glAttachShader(program, fs);

  //No need for shaders anymore
  glDeleteShader(vs);
  glDeleteShader(fs);

  //Set Attribute Locations
  glBindAttribLocation(program, 0, "vert");
  glBindAttribLocation(program, 1, "color");
  glBindAttribLocation(program, 2, "texcoord");

  //Link Program
  glLinkProgram(program);

  //Setup VAO and VBO
  glGenVertexArrays(1, &vao);
  glGenBuffers(1, &vbo);

  glBindVertexArray(vao);
  glBindBuffer(GL_ARRAY_BUFFER, vbo);

  glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat) * 9 * 6, vertices, GL_STATIC_DRAW);

  glEnableVertexAttribArray(0);
  glEnableVertexAttribArray(1);
  glEnableVertexAttribArray(2);

  glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 9 * sizeof(GLfloat), NULL);
  glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 9 * sizeof(GLfloat),(GLvoid*)(3*sizeof(GLfloat)));
  glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 9 * sizeof(GLfloat),(GLvoid*)(7*sizeof(GLfloat)));

  //Init TTF
  TTF_Init();
  
  //Open Font
  font = TTF_OpenFont("Ubuntu-Regular.ttf", 30);

  SDL_Color color = {0, 255, 255, 255};

  //Create Surface
  surface = TTF_RenderUTF8_Blended(font, "This is TEXT!", color);

  //Your format checker
  GLenum format = (surface->format->BytesPerPixel==3)?GL_RGB:GL_RGBA;

  //Create OpenGL Texture
  glGenTextures(1, &texture);
  glBindTexture(GL_TEXTURE_2D, texture);
  glTexImage2D( GL_TEXTURE_2D, 0, format, surface->w, surface->h, 0, 
              format, GL_UNSIGNED_BYTE, surface->pixels);

  //Set Some basic parameters
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

  //Set up Sampler
  glActiveTexture(GL_TEXTURE0);
  glBindTexture(GL_TEXTURE_2D, texture);

  uniformSampler = glGetUniformLocation(program, "myTextureSampler");
  //It defaults to using GL_TEXTURE0, so it's not necessary to set it
  //in this program it's generally a good idea.

  //-------------------------------------------------------------------------------------- 
  // DRAW STAGE
  //-------------------------------------------------------------------------------------- 

  glUseProgram(program);

  //glBindVertexArray(vao); - still in use

  glClear(GL_COLOR_BUFFER_BIT);

  glDrawArrays(GL_TRIANGLES, 0, 6);

  SDL_GL_SwapWindow(window);

  //Sleep for 2s before closing
  SDL_Delay(2000);
}